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Those most at risk of infection included infants and young children, the sick, and the elderly.

Further, some 7.5 per cent – or roughly 288,000 people – received drinking water that wasn't adequately monitored for these standards, and 8,700 were getting water that wasn't monitored at all.

More than 34,000 New Zealanders were also getting water with an "excessive" number of transgressions involving E. coli.

Overall ... most New Zealanders receive safe drinking-water. However some people, usually those in rural areas or smaller supplies, can't always access water of the same standard. This needs to change.

"The presence of E. coli in water indicates that the water has been contaminated with faeces and inadequately treated, or may result from contamination of the water during post-treatment distribution to the community," the report found.

"In either case, the presence of E. coli means that other faecal pathogens could be present in the water that pose a threat to public health."

On the back of a tightening of requirements for secure bores, which came after more than 5000 people fell sick in Havelock North's 2016 gastro outbreak , there was a jump in supplies failing to meet protozoal standards.

Under these standards – which monitored the effectiveness of treatment used to remove or inactivate cryptosporidium – the number of compliant supplies fell from 83.1 per cent to 74.8 per cent.

The report also found ongoing problems with a large proportion of the 493 small supplies covered.

Meanwhile, a total 84.7 per cent of those people were receiving water that complied with legislative requirements, while 99.3 per cent were being serviced by a supply that now had a water safety plan in place.

Around 98.9 per cent of people were drinking water that met chemical standards, with fluoride being the most commonly used, and serving some 2,232,000 New Zealanders.

"Overall, conclusions from the report are that most New Zealanders receive safe drinking-water," said the ministry's director of public health, Dr Caroline McElnay.

Protesters in a Walk for Water, a march from Havelock North to Hastings CBD, after the gastro outbreak in Havelock North in 2016. Photo / File

"However some people, usually those in rural areas or smaller supplies, can't always access water of the same standard. This needs to change.

"The ministry has written directly to those suppliers required to have a water safety plan and who're still failing to comply with the act."

The Government was continuing to push through 51 recommendations that stemmed from an inquiry following the Havelock North outbreak.

"Work is well underway to continue to drive the improvements we need for drinking-water supply, both in the short and long term."

'THIS IS AN ONGOING PROBLEM'

Michael Baker, a professor of public health at the University of Otago in Wellington, said too much of the picture was still missing.

Around 20 per cent of the population wasn't covered by the report – and it didn't account for the increased risk that those sub-standard smaller supplies posed to tourists or holidaymakers from the cities.

"This is an ongoing problem that really does need additional effort to understand."

Another glaring problem, he said, was that the report didn't addressing the mounting problem of nitrates in water – something which had been linked to colorectal cancer and other health risks.

"Yet there is very little testing for nitrates in the system at the moment – I understand that less than 1 per cent of supplies are actually monitored for it.

Otago University's Professor Michael Baker has called on the Government to set up a new centralised agency dedicated to ensuring the quality of drinking water. Photo / File

"That's based on testing from quite a few years ago that suggested it wasn't a major problem, but since then, there has been increasing knowledge that low and intermediate levels of nitrates in drinking water are associated with adverse health outcomes."

With dairy intensification, nitrate levels were rising in surface water, and probably also in an artesian waters, Baker said, and New Zealand was "well overdue" to carry out a national survey.

He also called on the Government to set up a new centralised agency dedicated to ensuring the quality of drinking water, as many other countries now had.

BY THE NUMBERS

• 97.7% of the report population (3,751,000 people) received drinking-water that achieved the bacteriological standards between 2017-18, an increase of 1.5% compared with the previous year.

• 84.7% of the report population (3,250,000 people in 329 supplies) received drinking-water that complied with all the legislative requirements.

• 99.3% (3,810,000 people in 481 supplies) received drinking-water from a supply with a water safety plan for which implementation has started.